Field of the Invention
The present invention relates to an engine valve for opening/closing an intake port or an exhaust port of a combustion chamber of an internal combustion engine, and further relates to a method of producing such an engine valve.
Description of the Related Art
In order to increase the rotation speed of an engine, it is essential to increase the response speed of an engine valve responsive to rotation of a cam by reducing the weight of the engine valve. Further, in the case where the output of the engine is increased, since the combustion temperature is increased, if the heat radiation performance of the engine valve is poor, the engine valve may be heated to a temperature beyond the heat resistant temperature. Therefore, in the case where the engine valve is used for the internal combustion engine which requires high speed rotation and high output, the engine valve needs to be excellent in lightweight property, and have sufficient heat radiation performance or heat resistance performance.
In this regard, Japanese Patent Publication No. 04-069495 proposes an engine valve including a hollow valve body and a core member loaded inside the valve body. The valve body is made of steel, and the core member is made of titanium or titanium alloy which has good heat resistance performance, and has a specific gravity smaller than that of steel. Therefore, in this engine valve, in comparison with the engine valve having a solid valve body (made of only steel), it is possible to achieve weight reduction without degrading the heat resistance performance.
Further, Japanese Utility Model Publication No. 60-034725 proposes an engine valve where a core member made of any of aluminum, aluminum alloy, magnesium, and magnesium alloy is loaded inside the valve body. Japanese Laid-Open Patent Publication No. 2012-097627 proposes an engine valve where metal sodium is sealed inside the valve body. In the engine valves described in Japanese Utility Model Publication No. 60-034725 and Japanese Laid-Open Patent Publication No. 2012-097627, metal having a small specific gravity and a large heat conductivity in comparison with steel is provided inside the valve body. Therefore, it is possible to achieve weight reduction and improve heat radiation performance in comparison with the engine valve having the solid valve body.